However, no studies have successfully identified reliable human TS markers. Stem cells have been identified in Butenafine hydrochloride diverse adult tissues and play a critical role in tissue homeostasis throughout life. Somatic stem cells are defined as undifferentiated cells because of their ability to both self-renew and differentiate to produce mature progenitor cells at the single cell level. In 1996, hematopoietic stem cells with immature characteristics were isolated from a specific cell population called side-population 
cells. SP cells have the unique ability to pump out DNA binding dye Hoechst 33342 via the breast cancer resistance protein1/ATP-binding cassette transporter, subfamily G. To date, SP cells have been isolated from several normal tissues, including blood, intestine, liver, lung, muscle, skin, uterus, testis, and mammary gland. The ability of SP cells to rapidly efflux Hoechst 33342 has been used to isolate SP cells by flow cytometry and cell sorting. In this study, we isolated and analyzed SP cells from a human trophoblast cell line, HTR-8/SVneo and human primary vCTB. By immunocytochemistry and gene expression analysis at the genome-wide level, SP cells were suggested to include vCTB stem cells/ progenitor cells. They showed long-term repopulating capability and differentiated into multiple trophoblast cell lineages in vitro. We also identified IL7R and IL1R2 as two excellent markers to separate SP population from non-SP population. Many human trophoblast cell lines have been established, which essentially originated from one of two sources: from normal tissues or from malignant tissues. For our purpose of studying villous cytotrophoblast progenitor cells, cancer cell lines were thought to be inappropriate because of their aberrant gene expression that developed in the process of carcinogenesis. Because of the Catharanthine sulfate absence of proper vCTB cell lines that precisely reflect vCTB in vivo, we first tested an immortalized human trophoblast cell line, HTR-8/SVneo, which is known to have originated from extravillous cytotrophoblast. Another trophoblast cell line, TCL1, which has also been used as an EVT cell line, was used for comparison with HTR-8/SVneo. HTR-8/ SVneo was established by transfection of human primary trophoblasts, which originated from first trimester villous explants, with a gene encoding simian virus 40 large T antigen to immortalize them. On the other hand, the other cell line, TCL-1, was established by retroviral expression of simian virus 40 large T antigen in primary culture of choriodecidua of a term placenta. A single cell was isolated from it and a clone that could repopulate for long term was established. It has been proposed that human placenta villi contain a population of stem cells with remarkable regenerative capability. In this study, HTR-8/SVneo was selected to analyze SP cells. Although many trophoblast cell lines have been established, no cell lines that faithfully reflect the features of vCTB are available. HTR-8/SVneo was generated from primary villous explants of early pregnancy. This suggests that HTR-8/SVneo is heterogeneous in terms of cell population. Several different trophoblast cell types including villous trophoblast and EVT were expected to be present in the original cell population. In fact, the expression profile of trophoblast differentiation markers demonstrated that HTR-8/SVneo included cells expressing vCTB, STB and EVT markers. Additionally, a genome-wide study revealed that HTR-8/SVneo had large differences in gene expression profile from primary EVT.